Introduction

Jet lag is a common condition that sometimes occurs after long distance. It occurs because your body finds it difficult to adjust to a new time zone.

Jet lag can disturb your sleep pattern, leaving you feeling drowsy and lethargic(lacking in energy). Jet lag often becomes more severe as more time zones are crossed.

Time zones

The world is divided into 24 time zones. The Greenwich Meridian (an imaginary line which passes through Greenwich, in London, and is used to help measure longitude) is the base. The clock changes by one hour for every 15 degrees travelled in either direction from the Greenwich Meridian.

Jet lag occurs after crossing a number of time zones which disrupts the body's normal 'circadian rhythm' (your body's natural 24-hour routine). This body clock controls when you need to sleep and when you are awake. It also affects:

• hunger
• digestion
• bowel habits
• urine production
• body temperature
• blood pressure

Your biological clock is normally synchronised with your local time so that you feel hungry in the morning and sleepy in the evening. However, after travelling across time zones, your body takes a while to adjust to a new daily routine.

See Jet lag - causes for more information about the circadian rhythm and the biological clock.

Who gets jet lag?

Anyone can get jet lag, regardless of how frequently they travel by plane. People of any age can develop the condition, although it is more common in those who are over 60 years of age.

Jet lag is thought to be less common in children and babies. However, there is not enough clear evidence to estimate how many children and babies are affected. 

Outlook

If you have had jet lag before, you are more likely to get it in the future. However, flying long distances does not necessarily result in jet lag. There are ways to help prevent the condition.

See Jet lag - prevention for more information about how to cope with jet lag, and ways of preventing it.

Although jet lag may be problematic for people who have to fly frequently, or who are travelling to an important meeting, or event, it does not cause any serious, or long-term, health problems.

Most people find that their jet lag symptoms pass within a few days without the need for treatment.

Symptoms

Symptoms of jet lag can vary from person to person. The severity of your symptoms will normally depend on how far you have travelled and how many time zones you have crossed.

Most people will only have symptoms of jet lag after crossing at least three time zones, although some people may get mild symptoms after shorter journeys.

Sleep disturbance

One of the most common symptoms of jet lag is a disturbed sleep pattern. Jet lag can often cause you to feel tired, but you may find that you cannot sleep at the correct times. For example, you may be awake during the night and sleep during the day.

As well as disturbed sleep, other symptoms of jet lag can include:

• indigestion
• constipation
• diarrhoea
• nausea
• loss of appetite
• difficulty concentrating
• feeling disorientated
• anxiety
• irritability
• memory problems
• clumsiness
• lack of energy
• light headedness
• confusion
• headaches
• sweating
• muscle soreness
• menstrual irregularities in women who often travel
• generally feeling unwell

Symptoms of jet lag will normally usually last for no more than a day or two, depending on how quickly your body is able to adjust to the new time zone. 

Causes

Circadian rhythm

Your circadian rhythm is your body's natural 24-hour routine, which is driven by a number of ‘biological clocks’ in your body. Jet lag occurs when your body's circadian rhythm is disrupted.

The biological clocks are found throughout your body and are made up of groups of cells that interact with each other. These cells are controlled by a ‘master clock’ in your brain that keeps the body clocks synchronised with one another.

Your body is used to a regular routine of light and darkness at certain times of the day. However, when you travel to a new time zone, this regular rhythm becomes disrupted.

Modern air travel makes it possible for you to travel across several different time zones in just a few hours. As a result of travelling so quickly, the body has to try to catch up, and re-establish its circadian rhythm. It takes time for your body to adjust to new times of light, darkness, and eating. Your body may also have to adjust to differences in temperature.

Oxygen levels

The oxygen levels in an aeroplane cabin are also thought to play a role in jet lag. Because air pressure is relatively low in an aeroplane cabin, the amount of oxygen you have in your blood is reduced.

A reduced amount of oxygen can affect your physical and mental abilities. For example, it can make you feel lethargic (lacking in energy) and dehydrated.

People with conditions such as heart disease, lung disease, or anaemia (where the red blood cells are not able to carry enough oxygen), may be more severely affected by this reduced amount of oxygen inside the cabin.

East and west

The symptoms of jet lag are normally more obvious when you travel east rather than west. This is because your body finds it easier to adapt to a slightly longer day (in the west) than a slightly shorter one (in the east).

Your body adapts better when travelling west because you are extending your day, rather than travelling east when you are shortening it. In other words, it is easier to delay sleep for a few hours than force yourself to sleep when you are not ready.

Sleep routine

People who have a strict sleep routine - for example, they go to bed at the same time each night - are more likely to be affected by jet lag. As babies and children are able to sleep at any time of the day, they tend to adjust to new time zones more easily, and are less likely to experience jet lag.

Other factors

There are a number of factors that can increase your likelihood of experiencing jet lag, or increase the severity of your symptoms. These factors include:

• dehydration (not drinking enough fluids)
• lack of sleep
• drinking alcohol
• stress
• being above 60 years of age increases the time it takes to recover from jet lag

Treatment

Prevention

Jet lag cannot be prevented but there are ways of reducing its effects. These are  outlined below.

Before you travel

Before travelling, you should:

• Change your sleep routine a few days before you are due to travel. If you are travelling east, go to bed an hour earlier than your usual time. If you are travelling west, go to bed an hour later. Try to adapt your sleeping routine with your destination in mind.  
• Get enough sleep before you are due to travel. Flying when you are tired can make jet lag worse.  
• Keep calm - airports can sometimes be stressful situations. Try and keep as calm and relaxed as possible because being stressed can make jet lag worse.
• Check in online - this can help to reduce stress and will enable you to relax as soon as you arrive at the airport.

During the flight

During the flight, you should:

• Drink plenty of fluids - also ensure that you are well hydrated before and after your flight.  
• Rest during the flight by taking short naps.
• Avoid alcohol - eat light meals and avoid drinking alcohol because it can make symptoms of jet lag worse. 
• Keep active - if you are flying long distances, walk around the cabin occasionally and regularly stretch your arms and legs when you are sitting down. This will also help to reduce the risk of developing a potentially serious condition called deep vein thrombosis (DVT).
• Change your watch when you board the plane so that it matches the time of your destination. This will help you to adjust more quickly to your new time zone.  
• Get some sleep - if it is night time at your destination, try to get some sleep. Some people find using ear plugs, or eye masks, helpful.

Short trips

If your trip only involves staying at your destination for a short time (less than three or four days) – for example, a business trip – it may be better to stay on ‘home time’. Arrange your activities and sleep to coincide with the time at home. This will reduce the chances of your body clock being disrupted.